Start the Car With a Dead Key Fob Battery

Last updated: June 12, 2026

The Hyundai i10 (Mk3/AC3, 2020–Present) is sold both as a turn-key city car on lower trims and, on Premium and higher specs, with the Smart Key proximity fob and a START/STOP button. When the fob’s CR2032 coin cell dies the remote-lock buttons and proximity unlocking stop, but the car can still read the key at point-blank range and start normally — or, on bladed-key cars, the ignition barrel reads the transponder directly.

Start a Smart Key i10 with a dead fob

If your i10 has the keyless Smart Key and a START/STOP button on the dash:

1. Get into the car using the emergency blade first (next section) and sit in the driver’s seat.
2. Press and hold the brake pedal down firmly.
3. Hold the Smart Key so the back face of the fob touches the START/STOP button directly.
4. With the fob pressed against it, push the START/STOP button.
5. The immobiliser reads the transponder through the button and the engine cranks and starts.

Turn-key i10 — the blade still starts it

Entry and SE trims use a conventional flip key with an ignition barrel. A flat coin cell only kills the remote-lock buttons; unlock the driver’s door with the blade, slide it into the barrel and start the car as usual. The transponder in the key head is energised by the barrel, so it works regardless of the coin cell.

Unlock the i10 with the emergency key blade

1. Slide the catch on the back of the Smart Key and pull the metal emergency blade out of the body.
2. At the driver’s door handle, insert the blade into the lock slot and turn to unlock.
3. The alarm may chirp until the car recognises the key — starting the engine cancels it.

Why a flat fob still starts the i10

The coin cell only powers the remote buttons and the proximity broadcast that lets you unlock and start without touching the fob. The chip that authorises the engine is a passive RFID transponder with no battery of its own — it is woken by the coil behind the START/STOP button (or the ignition barrel on turn-key cars). Because that chip never depends on the cell, the immobiliser can still verify the key when the fob is completely dead.

Replace the fob battery

The i10 Mk3 Smart Key uses one CR2032 3V lithium coin cell. Pull the emergency blade, then use it or a small coin to twist the case open at the seam. Lift out the old cell, fit the new one with the + side facing the same way, and click the halves back together. Remote locking and proximity start return immediately. A genuine Energizer or Duracell cell typically lasts two to three years.

Frequently Asked Questions

Does my i10 have keyless start?

Only Premium and higher trims came with the Smart Key and a START/STOP button. Entry and SE cars use a flip key with an ignition barrel and just need the blade.

Where exactly do I hold the fob to start it?

Press the back of the Smart Key flat against the START/STOP button itself, keep the brake down, then push the button with the fob still in place.

The remote stopped working but the car still starts — is that bad?

On a turn-key i10 that is normal: a flat cell disables only remote locking while the key transponder still starts the engine. Replace the CR2032 when convenient.

Why did the alarm sound when I used the blade?

Mechanical entry looks like a forced entry until the transponder is read. Starting the engine clears the alarm.

Which battery does the i10 Smart Key take?

A single CR2032 3V lithium coin cell, available from any supermarket or hardware shop.

If a warning light stayed on after the no-start, look it up on autodtcs.com to confirm it was just the fob and not an immobiliser fault.